Application of fungal laccase for heavy metals precipitation using tannin as a natural mediator

Abstract

Nowadays, natural compounds have generated innovative attention for metal removal and precipitation; here, a fungus was isolated from soil samples in tannin media for metal removal. The isolate was identified as ‘Albifimbria viridisʼ by morphology and amplification of specific sequence. The isolate produced high activities of laccase when induced with tannin. The cell-free supernatant with 50 U/ml laccase activities could remove nickel, cobalt, cadmium, and copper nitrate salts by 59.69%, 59.75%, 46.97%, and 66.79%, respectively, while the precipitation of crude enzyme and metal salts by Fourier transform infrared spectroscopy analyses showed that only 2 metal salts (Cobalt and Copper nitrate) are precipitated in oxide form. Tannin was used as a mediator for metal removal, and the data were supported using a zymogram with partially purified laccase and metal precipitation on polyacrylamide gel electrophoresis. A 66 KDa laccase can remove metals and tannin. The metal interaction by this isolated compared with Phanerochaete chrysosporium and Aspergillus niger. All studied fungi could biodegrade the tannin as sole carbon source; however, for maximum activities, the new isolate Albifimbria viridis was selected in further study. The purified fungus in this study is a herbicide and has a high activity of laccase. The precipitation of metals by the enzyme of grown fungus in tannic acid is reported for the first time, which promoted the functional importance of this fungus.